diff --git string.c string.c
index 9079387..47d6f42 100644
--- string.c
+++ string.c
@@ -4965,7 +4965,11 @@ rb_str_sub_bang(int argc, VALUE *argv, VALUE str)
                 repl = rb_obj_as_string(rb_yield(match0));
             }
             else {
-                repl = rb_hash_aref(hash, rb_str_subseq(str, beg0, end0 - beg0));
+                VALUE key = rb_str_subseq(str, beg0, end0 - beg0);
+                repl = rb_hash_aref(hash, key);
+                if (NIL_P(repl)) {
+                    repl = rb_hash_aref(hash, rb_to_symbol(key));
+                }
                 repl = rb_obj_as_string(repl);
             }
 	    str_mod_check(str, p, len);
@@ -5140,7 +5144,11 @@ str_gsub(int argc, VALUE *argv, VALUE str, int bang)
                 val = rb_obj_as_string(rb_yield(match0));
             }
             else {
-                val = rb_hash_aref(hash, rb_str_subseq(str, beg0, end0 - beg0));
+                VALUE key = rb_str_subseq(str, beg0, end0 - beg0);
+                val = rb_hash_aref(hash, key);
+                if (NIL_P(val)) {
+                    val = rb_hash_aref(hash, rb_to_symbol(key));
+                }
                 val = rb_obj_as_string(val);
             }
 	    str_mod_check(str, sp, slen);
diff --git test/-ext-/string/test_gsub.rb test/-ext-/string/test_gsub.rb
new file mode 100644
index 0000000..27eb350
--- /dev/null
+++ test/-ext-/string/test_gsub.rb
@@ -0,0 +1,18 @@
+require 'test/unit'
+require "-test-/string"
+
+class Test_StringGsub < Test::Unit::TestCase
+  def test_gsub_with_hash
+    hash = {'b'=>'B', 'c'=>'C'}
+    assert_equal("abcabc".gsub(/[bc]/, hash), "aBCaBC")
+    assert_equal("cbacba".gsub(/[bc]/, hash), "CBaCBa")
+    assert_equal("abcabc".gsub(/[ac]/, hash), "bCbC")
+  end
+
+  def test_gsub_with_symbol_key_hash
+    hash = {b: 'B', c: 'C'}
+    assert_equal("abcabc".gsub(/[bc]/, hash), "aBCaBC")
+    assert_equal("cbacba".gsub(/[bc]/, hash), "CBaCBa")
+    assert_equal("abcabc".gsub(/[ac]/, hash), "bCbC")
+  end
+end
diff --git test/-ext-/string/test_sub.rb test/-ext-/string/test_sub.rb
new file mode 100644
index 0000000..a70832c
--- /dev/null
+++ test/-ext-/string/test_sub.rb
@@ -0,0 +1,18 @@
+require 'test/unit'
+require "-test-/string"
+
+class Test_StringSub < Test::Unit::TestCase
+  def test_sub_with_hash
+    hash = {'b'=>'B', 'c'=>'C'}
+    assert_equal("abcabc".sub(/[bc]/, hash), "aBcabc")
+    assert_equal("cbacba".sub(/[bc]/, hash), "Cbacba")
+    assert_equal("abcabc".sub(/[ac]/, hash), "bcabc")
+  end
+
+  def test_sub_with_symbol_key_hash
+    hash = {b: 'B', c: 'C'}
+    assert_equal("abcabc".sub(/[bc]/, hash), "aBcabc")
+    assert_equal("cbacba".sub(/[bc]/, hash), "Cbacba")
+    assert_equal("abcabc".sub(/[ac]/, hash), "bcabc")
+  end
+end